Spent nuclear fuel has historically been stored in deep reservoirs of water, called spent fuel pools, within nuclear power plants. This spent fuel storage technology is often termed “wet storage.” Spent fuel pools at reactors are reaching their spent fuel capacity limits, causing concerns about the need to shut down reactors because there is no more room for the spent fuel. Dry nuclear spent fuel storage technology (termed “dry storage”) is deployed throughout the world to expand the capabilities of nuclear power plants to discharge and store nuclear spent fuel external to a reactor's spent fuel pool, thereby extending the operating lives of the power plants. Two classes of technology are used in dry spent fuel storage: metal casks with final closure lids that are bolted closed at the power plants after loading with spent fuel, and concrete storage casks containing metal canisters having canister final closure lids that are welded closed or sealed with mechanical methods at the power plants following spent fuel loading. This latter dry storage technology is referred to as canister-based concrete spent fuel storage. The concrete cask serves as an enclosure or overpack structure that provides mechanical protection, heat removal features, and radiation shielding for the inner metal canister that encloses the radioactive material. The use of this technology tends to have significant capital cost and other economic advantage over the use of metal cask technology for storage.
However, for transport of spent nuclear fuel, metal casks are still the preferred technology. For dry, spent nuclear fuel transport, two fundamental classes of technology are used: (i) metal casks with final closure lids (or lid) that are bolted closed at power plants or other facilities after loading of the spent fuel into open compartments of a separate structure nested within the cask body (termed the “basket”); this technology when used for spent fuel shipment is termed “bare fuel” transport; and (ii) similar metal casks with bolted final closure lids (or lid) having the metal canister used in dry storage within the cask body, the canister containing the basket structure and the final closure lid (or lids) installed at the power plants or other facility following spent fuel loading; this technology when used for spent fuel shipment is called “canistered fuel” transport.